1. Field of Invention
This invention relates to a process and a device for determining the viscosity or an associated quantity of a fluid or of magnetic particles in a fluid, especially of a microfluid, and uses of such a process or such a device.
2. Description of Related Art
U.S. Pat. No. 3,967,934 discloses a system and process for determining the coagulation time of blood. A test tube with blood is moved up and down, a metal ball in the blood within the test tube being kept in a vertical position by means of a steady-state magnetic field. When the test tube is moved up and down the blood flows around the metal ball. When coagulation of the blood takes place, the metal ball is deflected out of its defined vertical position. This deflection activates a photoelectric barrier and this is acquired as the coagulation time. The system is very complex, and in particular,r moving parts are necessary. The process is not suited for microfluidics, i.e., samples with a small volume, especially in the range of one milliliter or less. Likewise, no information about the progression of coagulation available.
Japanese patent publication JP 8-178823 discloses a process and a device for measuring the viscosity of viscous material. The measurement elements are fine, soft-magnetic particles, which are moved by an external steady-state magnetic field in the viscous material, for example, silicone or acrylic resin, in one direction. By means of a sensor which is based, for example, on the magnetoresistive effect, information about the moving magnetic particles is detected and the velocity and time of movement are measured to determine the viscosity. Compared to measurement elements which settle otherwise only by gravitation, a much shorter measurement time of roughly two to five minutes can be achieved. In the known process, the disadvantage is that several attempts with the addition of magnetic particles, which is necessary at the time, are needed in order to be able to achieve reasonable measurement accuracy. The process is accordingly complex and tedious. The process is not suited for microfluidics, i.e., samples with a small volume, especially in the region of one milliliter or less. Nor is any information about the progression of coagulation available.